The profound changes which occur in respiratory control mechanisms during early postnatal life are poorly understood. Abnormalities of this maturational process could predispose the neonate to Sudden Infant Death Syndrome (SIDS). The proposed research addresses the topic of respiratory control in the neonate with particular focus on the role of the carotid bodies. Ventilatory responses to 02 and C02 will be measured in unanesthetized 2, 6, and 10 day old carotid body-denervated and sham operated, control piglets. Thus effect of early postnatal age and sinus nerve section on ventilatory reflexes will be determined. In a separate protocol, 2, 6, and 10 day old piglets will first have their 02 and C02 sensitivities measured, and will then be anesthetized for measurement of sinus nerve activity during hypoxia and hypercapnia. Thus the ventilatory equivalent for sinus nerve activity will be determined at different stages of early postnatal life, and the contribution of peripheral chemosensory mechanisms to ventilatory drive during hypoxia and hypercapnia assessed as a function of age. Ultrastructural changes occurring in the carotid body during the first 10 day after birth, which may reflect the predicted functional maturation of the organ, will also be investigated. Carotid bodies will be excised from 2, 6, and 10 day old piglets and examined via electron microscopy. The long-term objective of this project is to characterize the maturation of the peripheral chemoreflexes in the piglet and to determine what role, if any, a malfunction of the carotid bodies may play in causing, or predisposing an infant to, SIDS.